1. Field of the Invention
This invention relates to a steering system for the rear wheels of a vehicle, and more particularly to a subsystem for selectively overriding the rear steering system prime mover so as to prevent the rear steering gear from exceeding a predetermined fractional component of its total angular range in the event that the operating condition of the vehicle warrants such limitation.
2. Disclosure Information
Rear wheel steering systems typically respond to steering of the front wheels of the vehicle. Certain systems respond to other vehicle inputs such as steering torque, vehicle speed, transmission gear or other parameters.
U.S. Pat. No. 4,671,523 discloses a system which immobilizes the rear steering gear in response to inputs from a steering torque sensor associated with the front wheels and a front wheel turn angle sensor. The system of the '523 patent limits the usefulness of the rear steering system because it is capable only of disabling the rear steering gear entirely; it will not serve to restrict the range of authority of the steering gear while still allowing a limited steering capability of the rear steering gear.
U.S. Pat. No. 4,566,711 and U.S. Pat. No. 4,705,135 disclose shaft-driven rear wheel steering systems in which a drive shaft couples the front and rear steering gears of a vehicle. The '711 and '135 patents further disclose motor operated devices for changing the front-to-rear steering ratio. In the event that these motor-driven ratio changing devices were to malfunction, a serious problem could be encountered by the driver because the driver could be unaware of the resetting of the front-to-front/rear steering ratio, and as a result, vehicle handling changes could cause a loss of vehicle control.
U.S. Pat. No. 4,105,086 and U.S. Pat. No. 4,657,102 disclose another type of system in which the power for actuating the rear wheel steering system is derived from a hydraulically controlled means. The '086 patent discloses a linkage-operated system, whereas the '102 patent discloses a purely hydraulically operated system. Each of the systems disclosed in the '086 and '102 patents suffers from a potential infirmity inasmuch as a malfunction in the control hydraulics of the systems could cause an unexpected slewing of the rear wheels in one direction or another, with concomitant loss of vehicle control.
It is an object of the present invention to provide a system for selectively limiting the range of authority of a rear wheel steering gear.
It is an advantage of the present invention that a steering system according to this invention will have a limited capacity to steer the rear wheels once the vehicle has exceeded a threshold speed.
It is a further advantage of the present invention that a rear wheel steering gear according to this invention will not impair vehicle control even if the steering gear's control system becomes disabled.
Other objects, features and advantages of the invention will become apparent to the reader of the specification.